Apparatus for moulding helical parts by compacting powdered materials

ABSTRACT

Apparatus for moulding helical parts by compacting powdered materials to be sintered comprising a pair of dies having helical profiles and movable axially one respect to the other and two plungers adapted to compact the powder in the corresponding die. After the compression, a die is axially withdrawn from the other with a rotational movement and the moulded part can be ejected from the other die.

United States Patent Signora Sept. 30, 1975 [54] APPARATUS FOR MOULDINGHELICAL 2,767,438 10/1956 Pingel 425/78 PARTS BY COMPACTING POWDERED3,020,589 2/1962 Maritano 425/78 3,118,183 l/l964 Gex et a1. 425/345 XMATERIALS 3,394,432 7/l968 Laurent 425/78 [75] Invent r; MaurizioSignora Palazzo 3,677,671 7/1972 Martin 1 425/78 Canavese, h l 3,677,6727/1972 Harrington l 1 425/78 3,694,127 9/1972 Takahashi et al.. 425/78 X[731 Asslgnee: Ing. C. Ohvetti & -p- Uffici 3,773,446 11 1973 130mm425/78 Brevetti, Ivrea, Italy 22 Filed; 14 973 Primary Examiner-J.Howard Flint, Jr.

Attorney, Agent, or FirmSchuyler, Birch, Swindler, [21] Appl. N03424,700 McKie & Beckett [30] Foreign Application Priority Data [57]ABSTRACT Dec. 29, 1972 112211) .1 71122/72 Apparatus for mouldinghelical parts y Compacting powdered materials to be sintered comprisinga pair of [52] U.S. Cl. 425/78; 425/352; 425/418 dies having helicalprofiles and movable axially one respect to the other and two plungersadapted to compact the powder in the corresponding die,

6 Claims, 13 Drawing Figures [58] Field of Search 425/78, 79, 344, 345,352, 425/353, 354, 355

[56] References Cited UNITED STATES PATENTS 2,767.428 10/1956 Pingel425/79 -5 73 e l E gen US. Patent Sept. 30,1975 Sheet 1 of7 3,909,167

US Patsnt Sept. 30,1975 Sheet 3 of7 3,909,167

Fig.6

US. Patent Sept. 30,1975 Sheet 4 of7 3,909,167

US. Patent Sept. 30,1975 SheetS 0f7 3,909,167

US. Patent Sept. 30,1975 Sheet 7 of? 3,909,167

Fig.13

APPARATUS FOR MOULDING I'IELICALv PARTS BY COMPACTING POWDERED MATERIALSBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to an apparatus for moulding helical parts bycompacting powdered materials to be sintered having two differenthelical profiles.

2. Description of the Prior Art Apparatus for moulding helical partssuch as gear wheels is known. A first known apparatus comprises a dieand two punches movable in opposed fashion to compress the powder in thedie. With this known appav SUMMARY OF THE INVENTION According to thepresent invention there is provided an apparatus for moulding helicalparts by compacting powdered materials to be sintered comprising a pairof dies having helical profiles and movable axially one with respect tothe other, in which one of the dies is rotatable with respect to theother during the axial movement, and two plungers adapted to compact thepowder in the corresponding die by axial movement into the die, thecompacted parts having two different helical profiles in correspondencewith the two dies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of ahelical part to be moulded;

FIG. 2 is a median section of a first embodiment of the invention in theinitial stage of its operation;

FIGS. 3 and 4 show the apparatus of FIG. 2 from which a number of partshave been omitted in two following stages of its operation;

FIG. 5 is a partial section taken on the line V--V of FIG. 2;

FIG. 6 is a median section of a second embodiment of the invention inthe initial stage of its operation;

FIGS. 7 and 8 show the apparatus of FIG. 6 from which a number of partshave been omitted in two following stages of its operation; g

FIG. 9 is a partial section take on the line lX-IXof FIG. 6; g 7

FIG. 10 is thesection of FIG. 9 in which the apparatus of FIG. 6 isprovided with a modification;

FIG. 11 isa median section of a third embodiment of the invention in theinitial stage of its operation;

FIG. 12 shows the apparatus of FIG. 11.. from which a number of partshave been omitted in a following stage of its operation; and

FIG. 13 is a median section of a fourth embodiment in the initial stageof its operation.

DESCRIPTIONOF THE PREFERRED EMBODIMENT According to a first embodiment,the moulding apparatus comprises an upper die 14 (FIG. 2) for mouldingthe toothing 11 (see also FIG. 1) and a lower die 15 for moulding thetoothing 12. The profiles of the dies 14 and 15 respectively conformwith the profiles of the toothings 11 and 12 of the gear 10 to bemoulded. The upper die 14 is fixed in manner known per se to an upperdie-bearing plate 17 and is provided on top with two pins 18perpendicular to the said upper die 14 and fast therewith. Four stopfeet 19 (only two thereof are shown in FIG. 2) project from the upperdie 14 on the top thereof and have their upper ends disposed in a planeparallel to the plane of the upper die 14. The plate 17 is fixed inknown manner to the frame 20 of the press operating the apparatus of theinvention, as a result of which the upper die 14 is fixed with respectto this frame 20. Two vertical guide columns 22 project below theplate17 and are fixed thereto in manner known per se.

The moulding apparatus moreover comprises a vertically disposed cam 23(see also FIG. 5) the profile of which is constituted by a helicalgroove 24 of V-shaped cross-section. The cam 23 is fixed to the plate 17by means of the screws 25. The cam 23 is engaged by a conical end 26 ofa cam-following pin 27 disposed radially with respect to the lower die15 and provided at its other end with a screw 29 by means of which it isfixed to the die 15. The inclination of the helix of the groove 24 issuch that when the die 15 is shifted vertically, as 'will be describedin the continuation of the present description, the pin 27 turns the dieat the same time so that the profile of the die 15 itself describes ahelix corresponding to its own helix and therefore corresponding to thatof the profile 12.

Thelower die 15 is arranged rotatably on a lower diebearing plate 30, towhich it is also linked in the vertical direction, by means of rollingbearings indicated generally by the reference 31 in'FIG. 2. The plate isslidable in the vertical direction on the columns 22 and is providedwith a pair of flanges 32 in engagement with a pin 33 of'a lever 35mounted on a pivot 36. A cam follower 37 of the lever 35 is kept incontact with a cam 38 by a 'spring 39. The cam 38 rotates cyclicallythrough the medium of a shaft 40.

With the lower die 15 there co-operates a hollow lowerplunger 42 havingits profile corresponding to the profile 12 of the gear 10 to bemoulded. The lower plunger 42 is fixed in known manner to a plungercarrier 43 which is rotatable on a support 44 by means of rollingbearings 45 indicated generally in FIG. 2. The support 44 is fixed bymeans of screws 47 to a lower mount 48 slidable in the verticaldirection in the frame '20. The mount 48 is provided with a pair offlanges 49 in engagement with a pin 50 of a lever 51 mounted on a pivot52. A cam follower 54 of the lever 51 is normally kept in contact with acam 55 by a spring 56. The cam-55 is also rotated-by the shaft 40.

A core 59 is housed in the cavity of the plunger 42 and is movablevertically with respect thereto for forming the hole 13. The verticalmovement of the core 59 is controlled by cam means not shown in thedrawings.

An upper plunger 60 can co-operate with the upper die 14, the upperplunger being internally hollow to permit the passage of the core 59 andhaving its profile corresponding to the profile 11 of the gear to bemoulded. The upper plunger 60 is linked to an upper plunger carrier 61in the vertical direction and is rotatable on the latter through themedium of rolling bearings indicated generally by the reference 62 inFIG. 2 and disposed between the upper plunger 60 and the upper plungercarrier 61 itself. The plunger carrier 61 is slidable in the verticaldirection in the frame and is provided with a pair of flanges 63 inengagement with a pin 64 of a lever 65 mounted on a pivot 66. A camfollower 67 of the lever 65 is normally kept in contact with a cam 68 bya spring 69. The cam 68 is rotated by a shaft 70 in synchronism with theshaft 40.

Always in engagement with the upper plunger 60 is a nut 72 belonging toa plate 73 and having a profile corresponding to the profile of theupper die 14. The plate 73 is connected to the upper plunger carrier 61by means of two vertical tie rods 74 which are provided with a stop head75 at the upper end and are fixed to the plate 73 by means of theirthreaded end. The tie rods 74 can slide in two guide apertures 77 in theplunger carrier 61, while the stop heads 75 are normally kept in contactwith one face of the plunger carrier 61 through the medium of twocompression springs 78. The plate 73 is moreover provided with twovertical holes 79 into which the two pins 18 of the upper die 14 caninsert themselves.

The apparatus shown in FIGS. 2 to 5 operates in the following manner. Atthe beginning of the working cycle, the lower die 15 is in the highestposition with its own top face in contact with the bottom face of theupper die 14. In this position, the cam 23 orients the pin 27 in theangular position in which the profile of the lower die 15 mates with theprofile of the upper die 14 in the plane of contact between theaforesaid dies 14 and 15. The lower plunger 42 is within the lower die15 and the core 59 is substantially level with the top face of the upperdie 14. The upper plunger 60 and the plate 73 are in the highestposition, so that charging means for the powder (which are known and notshown in the drawings) can be arranged above the upper die 14.

Before conventional means which are not shown in the drawings cause theshafts 40 and 70 to rotate for one revolution and in synchronism, thesecharging means charge the powder into the dies 14 and 15, after whichthey are removed from the apparatus. The shafts 40 and 70 then rotatethe cams 38, 55 and 68 in the direction indicated by the arrows in FIG.2. At first the cam 68 actuates the lever 65 in the direction in whichthe plunger carrier 61 is lowered and this lowers the upper plunger 60and at the same time the plate 73 through the medium of the springs 78.The plate 73 descends until it is arrested by the feet 19 (FIG. 3) ofthe upper die 14. At the instant when the plate 73 comes into contactwith the feet 19, the profile of the nut 72 is aligned with that of theupper die l4 by means of the pins 18, which are inserted in the holes 79during the last portion of the stroke of the plate 73.

The feet 19 serve to ensure that at each cycle the position of arrest ofthe plate 73 with respect to the die 14 is always the same, so as toavoid displacements between the profiles of the said die 14 and the nut72. In fact, if the plate 73 were to stop against the top face of thedie 14, the powder which may have dropped on to this face during thecharging stage could change this position of arrest from one cycle tothe other.

The upper plunger 60, on the other hand, continues to descend inopposition to the action of the springs 78, being rotated by the nut 72which is locked angularly by the pins 18, and enters the upper die 14 tocompress the powder. Substantially at the instant when the upper plungercomes into line with the top face of the die 14, the cam 55 (FIG. 2)actuates the lever 51 in the direction for raising the lower mount 48.The mount raises the lower plunger 42 (FIG. 3) in the opposite directionto the upper plunger 60 by means of the plunger carrier 43 and thesupport 44. During the strokes of the plungers 42 and 60, the core 59remains stationary.

The gear 10 is therefore moulded, the profile of the toothing 1 1 beingformed by the upper die 14, while the profile of the toothing 12 isformed by the lower die 15.

The moulded part must now be extracted from the moulding apparatus. Tothis end, the core 59 (FIGS. 2 and 4) is first lowered to clear the hole13. The cam 38 then allows the spring 39' to turn the lever 35anticlockwise. Through the medium of the plate 30, this lever lowers thelower die 15 below the gear 10 and at the same time the cam 23 rotatesthe die 15 by means of the pin 27, as a result of which the die 15releases the toothing 12 without damage. After the lower die 15 hasreleased the profile 12, the cam 55 allows the spring 56 to turn thelever 51 anticlockwise to lower the lower mount 48 and, therefore, thelower plunger 42. When the core 59, the lower die 15 and the lowerplunger 42 reach the position shown in FIG. 4, the cam 68 turns thelever in the direction for lowering the upper plunger 60 further toexpel the moulded part from the die 14. Conventional means not shown inthe drawings collect the gear 10 and remove it from the mouldingapparatus.

Completing the rotation of one revolution, the cams 38, 55 and 68 act onthe levers associated with them so as to bring the apparatus back intothe beginning-ofcyle position shown in FIG. 2, to receive a fresh chargeof powder. More particularly, the pin 27, co-operating with the cam 23,brings the profile of the lower die 15 back to mate with the profile ofthe upper die 14 in the plane of contact between the dies 14 and 15themselves.

It is necessary to observe that the groove 24 of the cam 23 is longerthan the vertical stroke of the lower die 15, so that this die is alwayslinked to the said groove 24. It is not necessary, however, that thegroove 24 be inclined throughout its length, but it is sufficient, inaccordance with what has been explained hereinbefore, that it beinclined only in the portion corresponding to the thickness of thetoothing l 1. Only in this portion, in fact, it is necessary for thelower die to rotate.

Moreover, a cam of the type described, having a helical profile, may beconveniently replaced, in the case in which it is desired to mould gearsthe toothing of which is of limited inclination and/or thickness, by a.

plane cam the profile of which is constituted by a simple rectilineargroove. A plane cam is convenient within the limits in which theinclination of the teeth of the gear to be moulded and its thickness aresufficiently small to permit adequate keeping of the cam-following.

pin to the profile of the cam, notwithstanding the tendency of the pinto leave the same because of the rotation imposed thereon by the camitself.

In a second embodiment, the upper die 14 (FIG. 6) is devoid of the pins18 and is provided with two vertical holes 100 (see also FIG. 9)symmetrical with respect to the axis of the said die 14 and in which twoguide columns 101 are slidably inserted. The upper die 14 is movable inthe vertical direction by means of an upper die-bearing plate 102 towhich it is rotatably connected by means of the rolling bearings 103indicated generally in FIG. 6. The plate 102 is slidable in the verticaldirection on two columns 104 and is provided with a pair of flanges 105in engagement with a pin 106 of a lever 107 mounted on a pivot 108. Acam follower 110 of the lever 107 is normally kept in contact with a cam111 by a spring 112. The cam 111 rotates cyclically through the mediumof the shaft 70.

The lower die is fixed in known manner to a plate 113 fixed in turn tothe frame and provided with two openings 114 in the form of curved slots(see also FIG. 9) to allow the passage of the columns 101. The columns104 are moreover fixed to the plate 113. The stroke of the lower plunger42 is controlled by a cam 115 by means of a lever 116 mounted on a pivot117 and normally in contact with the cam 115 through the action of aspring 116'. The lever 116 comprises a pin 125 and a cam follower 126.

The cam 23 (see also FIG. 9) and the pin 27 are fixed to the upper die14 and the frame 20,'respectively. The nut 72 is fixed in conventionalmanner to a guide plate 118 similar to the plate 73 already described.The plate 118 is secured angularly with respect to the upper die 14 bythe two columns 101, the threaded upper ends of which are fixed to theplate 118 itself by means of two nuts 119. In FIG. 6 the columns 101 andthe openings 114 are shown for clarity in the median plane of theapparatus. In reality, they are disposed in a plane at 45 with respectto this median plane, as shown in FIG. 9, for the purpose of having alarger space available for charging the powder and for extracting themoulded part. The plate 118 (FIG. 6) is supported by a plate 120, towhich it is linked in the vertical direction and on which it isrotatable by means of the rolling bearings 121 indicated generally inFIG. 6. The plate 120 can be shifted vertically by the upper plungercarrier 61 by means of the tie rods 74 and the springs 78. The stroke ofthe upper plunger carrier 61 is controlled by a cam 121 by means of alever 122 mounted on a pivot 127 and the spring 123. The lever 122comprises a pin 128 and a cam follower 129.

The apparatus shown in FIGS. 6 to 9 operates in the following manner.FIG. 6 shows the apparatus at the beginning of the working cycle, whenthe upper die 14 is in contact with the lower die 15 and its profilemates with the profile of the lower die 15 in the plane of contactbetween the two dies themselves.

After the charging of the powder has been effected, the cam 121 turnsthe lever 122'in the direction in which the plunger carrier 61 islowered, so that the carrier lowers the upper plunger 60 (FIGS. 6 and 7)and the plate 1 18 until the latter is arrested by the feet 19. In thisposition, the profile of the nut 72 is aligned with that of the upperdie 14 through the medium of the columns 101. After the arresting of theplate 118, the upper plunger 60 continues to descend, being rotated bythe said plate 1 18, and enters the upper die 14, compressing the powderagainst the lower plunger 42, which is urged at the same time in theopposite direction by means of the cam 115 and the lever 116.

The moulded part must now be extracted from the moulding apparatus.First, the core 59 (FIGS. 6 and 8) is lowered to clear the hole 13. Thecam 111 then allows the spring 112 to turn the lever 107 clockwise andthe lever raises the plate 102 and the latter raises the upper die 14and the plate 118. The upper die 14 and the plate 118 are rotated at thesame time by the cam 23, which slides on the pin 27, so that thetoothing 11 is disengaged without damage. After the upper die 14 hasreleased the moulded part, the cam 121 allows the spring 123 to turn thelever 122 to raise the upper plunger 60 and the plate 118 to thebeginning-of-cycle position (FIG. 6), while the upper die 14 (FIG. 8) isarrested substantially at the height of the pin 27. Beyond thisposition, the plate 118 moves vertically guided by the columns 101.

The cam then allows the spring 116' to turn the lever 116 in thedirection for raising the lower mount 48 and therefore also the lowerplunger 42, which expels the moulded part from the lower die 15. Knownmeans (not shown in the drawings) extract the moulded part from themoulding apparatus. The cycle is therefore at an end and the cams 111,115, 121 act on the respective levers to bring the apparatus back to thebeginning-of-cycle configuration shown in FIG. 6. More particularly, thecam 23, co-operating with the pin 27, brings the profile of the upperdie 14 back to match or mate with the profile of the lower die 15 intheir plane of contact.

It is necessary to observe that the inclination of the helix of the cam23 is greater than the inclination of the teeth of the part to bemoulded, the distance between the cam 23 and the axis of the dies beingalways greater than the radius of the part to be moulded. When parts inwhich the toothing has a considerable inclination are to be moulded, theinclination of the groove 24 may assume very high values, so that thefriction between the cam 23 and the pin 27 does not allow the cam 23 tocause the die associated therewith to rotate. To obviate thisdisadvantage, the apparatus according to the invention comprises amechanism, indicated generally by the reference in FIG. 10, which isadapted to compensate the friction between the pin 27 and the cam 23during their relative movement. In FIG. 10, the mechanism 150 is shownfitted to the apparatus in the form illustrated in FIGS. 6 to 9.

The mechanism 150 comprises a double-acting hydraulic (or pneumatic)cylinder 152 which is fixed to the top face of the upper die-bearingplate 102 by known means not shown in the drawings. The cylinder 152 isprovided with two inputs'153 and 154 for the pressure oil for producingthe movements of a piston 155 in the two directions. Moreover, aconnecting rod 157 is disposed between the cam 23 and the rod 158 of thepiston 155 to transmit the force exerted by the pressure oil on thepiston 155 to the cam 23. The connecting rod 157 is pivoted at one endto a pin 159 projecting from the cam 23 itself and fast therewith and ispivoted at the other end to the end of the rod 158. Known means notshown in FIG. 10 are provided for varying the pressure of the oil inaccordance with the force it is intended to exert by means of the piston155 on the cam 23 and for commanding the admission thereof through oneor the other of the inputs 153 and 154.

At the instant when the cam 111 (FIG. 6) enables the plate 102 to raisethe upper die 14 to release the compacted part, oil under pressure isintroduced into the cylinder 152 (FIG. 10) through the input 153 or 154,according to whether the upper die 14 must rotate clockwise oranticlockwise, respectively. The force exerted on the cam 23 by thepiston 155 facilitates the sliding of the cam 23 itself on the pin 27inasmuch as it compensates the friction between these lastmentioned twoelements. The pressure of the oil may be predetermined in accordancewith the inclination of the groove 24 of the cam 23.

The moulding apparatus in the form shown in FIGS. 2 to may also includethe mechanism 150. In this case, the cylinder 152 is fixed to the lowerdie-bearing plate 30 and produces the rotations of the lower die 15 byrotation of the pin 27.

According to a third embodiment, the moulding apparatus comprises twolocking pins 170 and 171 (FIGS. 11 and 12) respectively controlled bytwo doubleacting and simultaneously and oppositely operated pneumaticcylinders 172 and 173. The apparatus shown in FIGS. 11 and 12 issubstantially the apparatus of FIG. 2, in which the locking pins 170 and171 have been substituted for the cam 23 and the pin 27. Moreover, thecam 55 has been replaced by another cam 174 of different profile. InFIG. 11, those parts of the apparatus which are not shown are the sameas the corresponding parts shown in FIG. 2.

The locking pins 170 and 171 are disposed radially with respect to thedies and plungers and have their ends substantially conical toco-operate respectively with two corresponding conical seats 175 and 176in the lower die 15 and the support 44, respectively. The cylinder 172is fixed to the lower die-bearing plate 30, while the cylinder 173 isfixed to a pillar 177 attached in turn to the lower mount 48, so thatthe cylinder 173 is connected rigidly to the said lower mount 48. Knownmeans not shown in the drawings are arranged for simultaneous andopposite operation of the cylinders 172 and 173.

The apparatus shown in FIGS. 11 and 12 operates in the following manner.In FIG. 11 the apparatus is illus-' trated at the beginning of the cyclewhen thedies 14 and 15 are in contact, the locking pin 170 is engaged inthe seat 175, while the locking pin 171 is disengaged from the seat 176.The locking pin 170 is arranged so as to lock the lower die 15 in theangular position in which its profile coincides with the profile of theupper die 14 in the plane of contact between the said two dies. The cams174 and 68 actuate the plungers 42 and 60 in an identical manner to thathereinbefore described with reference to FIGS. 2 to 5, in order tocompact the powder.

At the instant when the compression is at an end, the cylinder 172 (FIG.12) disengages the locking pin 170 and at the same time the othercylinder 173 engages the locking pin 171 in the seat 176. The lower die15 is now free to rotate, while the lower plunger 42 is rigidly fixed tothe lower mount 48.

To effect the extraction of the moulded part, the core 59 is firstlowered below the part and then the cam 38 actuates the lower die 15.The latter descends below the moulded part and at the same time isrotated by the lower plunger 42, thus disengaging the profile 12 withoutdamage. Thereafter, the core 59, the plunger 42 and the die descendsubstantially to the same position which is shown in FIG. 4. The cam 68(FIGS. 2 and 11) then actuates the upper plunger 60, which expels themoulded part from the upper die 14, similarly to what has already beendescribed with reference to FIGS. 2 to 5.

When the part has been extracted from the moulding apparatus by theabove-mentioned known means (not shown in the drawings), the lower die15, the lower plunger 42 and the core 59 are brought back to thebeginning-of-cycle position in the following manner. The plunger42 isenabled by the cam 174 to return to the end-of-compression positionshown in FIG. 12, while the lower die 15 is enabled by the cam 38 tobring itself into contact with the upper die 14. When the lower die 15is arrested against the upper die 14, the profiles of the two diescoincide in their plane of contact, since the lower punch 42 is in theposition shown in FIG. 12. The cylinder 173 then disengages the lockingpin 171, releasing the lower plunger 42, while the cylinder 172 engagesthe other locking pin in the seat 175, locking the lower die 15. The cam174 then allows the lower plunger 42 to return to the beginning-of-cycleposition shown in FIG. 11. The powder is charged and the plungers 42 and60 effect the compression thereof in the manner already described withreference to FIGS. 2 to 5.

The lockings pins 170 and 171 (FIG. 13) may also be fitted, insubstitution for the cam 23 and the pin 27, to the embodiment of theinvention described with refer.- ence to FIGS. 6 to 9. The apparatusshown in FIG. 13 is substantially that shown in FIG. 6, from which thecam 23 and the pin 27 have been removed and to which the aforesaidlocking pins 170 and 171 have been added. The pneumatic controlcylinders 172 and 173 (FIG. 13) are fixed to the upper die-bearing plate102 and the plate 120, respectively. The locking pin 170 is.

neously unlocks the upper plunger 60. At the instant when the end of thecompression is reached, the locking pin 170 unlocks the upper die 17 andat the same time the locking pin 171 locks the upper plunger 60.

Parts different from the herringbone gear of FIG. 1 can also be mouldedwith the apparatus of the invention. For example, it is possible. tomould drum cams provided with two differently inclined helical profiles.which are off-set and arranged on opposite sides with respect to a planeperpendicular to the axis of the cams.

It is clear that modifications and additions may be made in theapparatus of the invention without departing from the scope of theinvention itself. For example, the plungers and the rotatable die may berotated during their axial movement by means different from thosehereinbefore described. For instance, this may be done by means of aworm wheel and worm pair, a rack, or with pairs of helical ring gears. I

Moreover, the apparatus may comprise means for locking the dies duringthe compression of the powder. For example, this may be done by means ofa diepressing plate connected to the plunger co-operating with themovable die through the medium of a flexible coupling so as to be causedto bear resiliently against the movable die during the compression inorder to secure it positively.

I claim:

1. Apparatus for moulding helical, gear wheels by compacting powderedmaterials to be sintered, each wheel including two portions with theteeth inclined in opposite directions, said apparatus comprising:

a machine frame;

a pair of separate dies associated with said two portions each havingone helical profile corresponding to the inclination of the associatedportion of the helical gear wheel;

means for mounting one of said dies stationary with respect to saidframe;

a plate rotatably mounting the other one of said dies;

shifting means for shifting said plate in an axial direction withrespect to said dies so as to reciprocate the rotatably mounted diebetween a first position in which it is in contact with the stationarydie to a second position in which it is removed from said stationarydie;

a pair of plungers associated with said dies, each one having a helicalprofile in accordance with the inclination of the helical profile of theassociated die;

a pair of supports associated with said plungers, each of said supportsrotatably mounting one of the associated plungers;

means for moving said supports in said axial direction to cause saidplungers to compact the powder in the associated die, and

cam means for causing said rotatable die to rotate during its saidshifting movement in accordance with the helix of its own profile,whereby said rotatable die can be removed after the powder compressionfrom the relevant portion of compacted gear wheel.

2. Apparatus according to claim 1, wherein said stationary die normallycontacts said rotatably mounted die in a horizontal plane and issuperimposed on said rotatably mounted die, the helical profile of theplunger associated with the rotatably mounted die constantly engagingthe helical profile of the rotatably mounted die, and comprising athreaded member constantly in engagement with the helical profile of theplunger associated with the stationarily mounted die and connected tothe associated support so as to be reciprocably brought in contact withsaid stationarily mounted die and removed thereform concomitantly withthe associated plunger, and locking means for positively positioningsaid member in an angular fixed position when said member contacts saidstationarily mounted die.

3. Apparatus according to claim 1, wherein the cam means comprise a camwith a helically inclined groove and a cam follower disposed radiallywith respect to the dies and engaging in the groove.

4. Apparatus according to claim 1, comprising a double acting hydrauliccylinder adapted to transmit to the rotatably mounted die, throughintermediate means, a torgue commensurate to the value of the frictionalcouple between the cam and the cam follower during said shifting,whereby the friction between the cam and the cam follower is reduced.

5. Apparatus according to claim 1 comprising elements engagable forlocking respectively the rotatable die and the plunger associatedtherewith, and a pair of simultaneously and oppositely operateddouble-acting hydraulic cylinders for alternately actuating said lockingelements so as to alternately positively lock and release said rotatabledie and said associated plunger.

6. Apparatus according to claim 5, wherein said locking elements areformed by a pair of pins, the first of the locking pins being disposedradially with respect to the dies to introduce itself into acorresponding seat in the rotatable die, the cylinder associated withthe first locking pin being fixed to the said plate, the second of thesaid locking pins being disposed radially with respect to the dies tointroduce itself into a corresponding seat of the plunger associatedwith the rotatable die, the cylinder associated with the second lockingpin being fixed to the mount controlling the plunger associ ated withthe rotatable die.

1. Apparatus for moulding helical gear wheels by compacting powderedmaterials to be sintered, each wheel including two portions with theteeth inclined in opposite directions, said apparatus comprising: amachine frame; a pair of separate dies associated with said two portionseach having one helical profile corresponding to the inclination of theassociated portion of the helical gear wheel; means for mounting one ofsaid dies stationary with respect to said frame; a plate rotatablymounting the other one of said dies; shifting means for shifting saidplate in an axial direction with respect to said dies so as toreciprocate the rotatably mounted die between a first position in whichit is in contact with the stationary die to a second position in whichit is removed from said stationary die; a pair of plungers associatedwith said dies, each one having a helical profile in accordance with theinclination of the helical profile of the associated die; a pair ofsupports associated with said plungers, each of said supports rotatablymounting one of the associated plungers; means for moving said supportsin said axial direction to cause said plungers to compact the powder inthe associated die, and cam means for causing said rotatable die torotate during its said shifting movement in accordance with the helix ofits own profile, whereby said rotatable die can be removed after thepowder compression from the relevant portion of compacted gear wheel. 2.Apparatus according to claim 1, wherein said stationary die normallycontacts said rotatably mounted die in a horizontal plane and issuperimposed on said rotatably mounted die, the helical profile of theplunger associated with the rotatably mounted die constantly engagingthe helical profile of the rotatably mounted die, and comprising athreaded member constantly in engagement with the helical profile of theplunger associated with the stationarily mounted die and connected tothe associated support so as to be reciprocably brought in contact withsaid stationarily mounted die and removed thereform concomitantly withthe associated plunger, and locking means for positively positioningsaid member in an angular fixed position when said member contacts saidstationarily mounted die.
 3. Apparatus according to claim 1, wherein thecam means comprise a cam with a helically inclined groove and a camfollower disposed radially with respect to the dies and engaging in thegroove.
 4. Apparatus according to claim 1, comprising a double actinghydraulic cylinder adapted to transmit to the rotatably mounted die,through intermediate means, a torgue commensurate to the value of thefrictional couple between the cam and the cam follower during saidshifting, whereby the friction between the cam and the cam follower isreduced.
 5. Apparatus according to claim 1 comprising elements engagablefor locking respectively the rotatable die and the plunger associatedtherewith, and a pair of simultaneously and oppositely operateddouble-acting hydraulic cylinders for alternately actuating said lockingelements so as to alternately positively lock and release said rotatabledie and said associated plunger.
 6. Apparatus according to claim 5,wherein said locking elements are formed by a pair of pins, the first ofthe locking pins being disposed radially with respect to the dies tointroduce itself into a corresponding seat in the rotatable die, thecylinder associated with the first locking pin being fixed to the saidplate, the second of the said locking pins being disposed radially withrespect to the dies to introduce itself into a corresponding seat of theplunger associated with the rotatable die, the cylinder associated withthe second locking pin being fixed to the mount controlling the plungerassociated with the rotatable die.